The compaction properties is of importance in producing moulds of a suitable compactness. A loosely compacted (i.e. too low compaction ratio) mould will easily be damaged during handling before casting or during the casting operation itself. A low compacted mould might thus result in defective castings or in leaks of molten metal damaging the equipment. On the other hand an excessively compacted (i.e. too high compaction ratio) mould will have a low gas permeability consequently endangering entrapment of gases in the castings, thus creating porosities or even hazardous mould blow-outs.